Technologies using an unmanned aerial vehicle (UAV) in surveying are publicly known. The UAV used in these technologies may be mounted with a location-measuring device using a global navigation satellite system (GNSS) (called a “GPS receiver”), an inertial measurement unit (IMU), an altimeter, and a camera. Such a UAV may be made to photograph the ground while flying along a predetermined path in aerial photogrammetry or in other surveying.
Photogrammetry requiring no airphoto signals or using a reduced number of airphoto signals greatly depends on accuracy of location data of the camera. The UAV can locate its own location using the GNSS, but this locating is independent positioning having a positioning accuracy of approximately 1 meter in a horizontal direction and approximately 3 meters in a vertical direction, which does not achieve the accuracy required in photogrammetry. A UAV may be mounted with a more highly accurate location measuring device that can perform relative positioning using a GNSS. However, this concept is difficult to apply to a general purpose UAV in consideration of weight and electric power consumption of the device. To solve these problems, a total station (TS) may be used to track a UAV in flight and locate the UAV by using its laser distance measuring function (for example, refer to US2014/0210663).
This method of tracking the UAV by the TS uses an automatic target-tracking function of the TS. In this technique, laser light for searching is used to capture and track the UAV. The UAV has a reflective prism that reflects the laser light for searching, back in the incident direction, and the TS detects light reflected from the reflective prism to track the UAV.